<!DOCTYPE html>
<html>
<body>

    <br><br><br><br><br><br><br><br><br><br><br>

 
    <style>
        .tooltip {
            position: relative;
            display: inline-block;
            border-bottom: 1px dotted black;
        }
    
        .tooltiptext {
            visibility: hidden;
            opacity: 0;
            width: 120px;
            background-color: #555;
            color: #fff;
            text-align: center;
            border-radius: 6px;
            padding: 5px 0;
            position: absolute;
            z-index: 1;
            bottom: 125%;
            left: 50%;
            margin-left: -60px;
            transition: opacity 0.3s;
        }
    
        /* 三角形  */
        .tooltiptext::after {
            content: "";
            position: absolute;
            top: 100%;
            left: 50%;
            margin-left: -5px;
            border-width: 5px;
            border-style: solid;
            border-color: #555 transparent transparent transparent;
        }
    
        .tooltip:hover .tooltiptext {
            visibility: visible;
            opacity: 1;
        }
    </style>
    <div class="tooltip">Hover over me Tooltip
        <span class="tooltiptext">Tooltip text</span>
    </div>



    

<xmp style="font-size: 22px; font-weight: bolder;  margin-bottom: 66px;  color: black;  font-family: '微软雅黑';">

    必知必会
    
    <div class="tooltip">Hover over me Tooltip
        <span class="tooltiptext">Tooltip text</span>
    </div>

    .tooltip {
        position: relative;
        display: inline-block;
        border-bottom: 1px dotted black;
    }

    .tooltiptext {
        visibility: hidden;     => 先隐藏起来
        opacity: 0;
        width: 120px;
        background-color: #555;
        color: #fff;
        text-align: center;
        border-radius: 6px;
        padding: 5px 0;
        position: absolute;
        z-index: 1;
        bottom: 125%;
        left: 50%;
        margin-left: -60px;
        transition: opacity 0.3s;
    }

    /* 三角形  */
    .tooltiptext::after {
        content: "";
        position: absolute;
        top: 100%;
        left: 50%;
        margin-left: -5px;
        border-width: 5px;
        border-style: solid;
        border-color: #555 transparent transparent transparent;
    }

    .tooltip:hover .tooltiptext {
        visibility: visible;
        opacity: 1;
    }


   
    
</xmp>

</body>
</html>